The present invention relates to methods of lining the internal surface of a pipe, in particular to methods of lining the internal surface of an existing underground pipe.
There has been known a no-excavation underground pipe lining method in which the internal surface of an existing underground gas pipe, water pipe, etc. are lined with a resin without the necessity of any trenching or excavation. For example, a gas service pipe is buried underground branching from a gas main and extending to a user's house. In the method called no-excavation underground pipe lining, there are substantially two steps involved. In the first step, a pressurized liquid is used to produce a pushing force to introduce a necessary amount of resin into the service pipe through an open end thereof and to move the resin through the pipe until the front end of the resin plug flow reaches an inner end (a position branching from the gas main) of the pipe. In the second step, a suction force is used to suck the resin back from the inner end so as to line the internal surface of the pipe with the resin.
In the above first step, prior to introducing the resin into the pipe, a lining pig is at first inserted into the pipe so that it is located in the front of the resin plug flow while the resin is moved forward. In the above second step, such a lining pig serves to even a resin lining layer formed on the internal surface of the pipe so as to obtain a uniform thickness for the resin layer along the entire length of the pipe.
However, since a gas service pipe usually involves a tee member having a recess portion or involves a larger diameter portion along the length thereof, the lining pig is easy to enter or drop into these places, resulting in a problem that there would be no lining pig which can be used to produce a uniform resin lining layer on the internal surface of the pipe.
Further, since a gas service pipe may also involve a narrow-passing section such as valve along its length, it will be difficult for a conventional lining pig to pass therethrough. As a result, a desired lining treatment proves to be impossible.
Moreover, in the above first step, after the resin has been introduced into the pipe, a resin transporting pig, a liquid absorbing material and a liquid blocking pig are inserted behind the resin, so that the pressurized liquid is prevented from mixing into the resin while the resin is moved forward and backward in the pipe. But, a conventional liquid blocking pig sometimes proves to be insufficient to prevent a liquid from mixing into the resin, resulting in a liquid-containing resin that has a deteriorated adhesive property and hence can not adhere to the internal surface of the pipe.